Field of the Invention
The present invention relates to a process for producing biomethane intended for supplying a natural gas network from a plurality of biogas production plants, comprising the steps of producing, storing, purifying to biomethane and supplying the network, and also to a set of devices for the implementation of the process.
Related Art
Within the context of the upgrading thereof, biomethane—as a renewable substitute for natural gas that has the same properties as the latter—may be injected into a natural gas distribution or transport network that makes it possible to connect gas producers and consumers.
A natural gas distribution or transport network makes it possible to supply consumers with natural gas. The network is maintained at a pressure between 2 and 6 bar for distribution, 15 and 25 bar for medium-pressure distribution and 25 and 80 bar for transport.
Biogas is a gas produced by the natural or controlled fermentation of plant or animal organic matter (methanization). It predominantly contains methane (CH4) and carbon dioxide (CO2), but also, in smaller proportions, water, nitrogen, hydrogen sulphide, oxygen, and also other organic compounds, in trace amounts.
Depending on the organic matter and the techniques used, the proportions of the components differ, but on average biogas comprises, as dry gas, from 30% to 75% methane, from 15% to 60% CO2, from 0 to 15% nitrogen, from 0 to 5% oxygen and trace compounds.
Added more recently to the upgrading—mainly on-site or nearby—of biogas is that of biogas purified to the specifications of natural gas. Biomethane may be used as a non-fossil substitute for natural gas thus supplementing natural gas resources with a renewable portion produced at the heart of territories. It can be used for exactly the same uses.
The methods of upgrading biomethane are determined as a function of local contexts: local energy requirements, possibilities of upgrading as biomethane fuel, existence nearby of networks for distributing or transporting natural gas in particular. Creating synergies between the various operators working in a territory (farmers, manufacturers, public authorities), the production of biomethane helps territories to acquire greater energy self-sufficiency.
In order to produce and use biomethane as renewable natural gas in natural gas networks, two main players are involved: the first of these players is the biomethane producer, the second player is the natural gas distributor who manages the gas network.
In order to have the option of injecting biomethane into an existing gas network, it is necessary to provide the plant with a metering station (for example GRdF or GRT Gaz [French gas distribution network companies] injection posts) and to provide the connection to the nearby network. The pressure of the gas in the network may vary and will sometimes require an additional compression in order to permit the injection.
Therefore, when a biogas producer wishes to use his gas to produce biomethane for injecting into a network, he has to face, in all cases, the installation and maintenance costs of the injection system; also sometimes, in certain cases, additional constraints are imposed on the biogas producer:                technical constraints of the network operator which require sizeable investments, and/or        minimum volume of biogas to be produced which often exceeds the production capacity of small producers (agricultural producers, private producers or others).        
To date, no solution exists for these small biogas producers which enables them to produce biogas intended for injection into a natural gas network.
There is therefore a need for a solution for producing biomethane—available for being injected into a network—that makes it possible to treat a plurality of small-volume biogas productions with a view to producing biomethane for a limited cost for the producers.
There is also a need, for the natural gas network managers, to have sufficient and reliable supplies of biomethane with a view to increasing the portion of renewable gas in the gas circulating in the network.
There is therefore a need for a solution that provides the producers with the upgrading of their biogas productions that are too small to be upgraded individually and which provides supplies of biomethane for a natural gas distribution or transport network from a plurality of biogas productions.